The invention relates to the fluid process measurement and control industry. The process measurement and control industry employs process variable transmitters to remotely monitor process variables associated with fluids such as slurries, liquids, vapors, gasses, chemicals, pulp, petroleum, pharmaceuticals, food and other food processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties.
FIG. 1 illustrates a process flow device 50 for measuring process variables, such as pressure and flow. Device 50 includes a flow plate 52 clamped between pipe flanges 54, 56 and a remote temperature sensor 60. Mass flow rate for fluid flow is a function of:
Q=KaYFa{square root over (2gc(xcex94p)(xcfx81))}
where:
Qxe2x80x94is the mass flow rate;
xcfx81xe2x80x94is the density of the fluid;
xcex94pxe2x80x94is the differential pressure across a flow constriction;
axe2x80x94is the cross sectional area of the orifice;
Yxe2x80x94is a gas expansion factor;
Faxe2x80x94is the area factor for thermal expansion of the orifice;
gcxe2x80x94is a unit conversion factor; and
Kxe2x80x94is a flow coefficient.
Density xcfx81 of the fluid is a function of the temperature and pressure of the fluid. For compressible fluids, such as gases, pressure has a relatively large impact upon fluid density (xcfx81). Temperature variations influence mass flow rate calculation since mass flow rate is a function of the density xcfx81 as well as the profile and dimension of the flow constriction. The profile and dimensions of the flow constriction change with temperature variations due to thermal expansion. In particular, fluid density is a function of at least temperature and metal orifice plates expand and contract with temperature changes.
In prior flow plate applications, temperature was measured remote from the flow plate 52. The remote temperature measurement was used to estimate the temperature proximate the flow constriction. The remote temperature measurement required separate pipe connections creating increased maintenance and installation complexity. Such added complexity increased field installation time due to increased assembly and testing time. Additionally, each sealed interface provides a potential location for the development of leaks due to the significant static pressure generally present within the pipe. Such leaks, also known as fugitive emissions are undesirable.
A temperature sensing channel is disposed proximate a flow plate to provide reduced field installation time, cost, and complexity while potentially increasing device accuracy and longevity. Embodiments of the invention relate to a flow plate and a temperature sensor disposed proximate the flow plate in a sensing channel.